1. Field of the Invention
The present invention relates to methods for completing wells, such as hydrocarbon and water wells. Particularly, the present invention relates to junctions in multilateral wellbores. More particularly, the invention relates to an apparatus and methods for forming and completing junctions, especially junctions designed for solids exclusion.
2. Description of the Related Art
Hydrocarbon wells are typically formed with a central wellbore that is supported by steel casing. The steel casing lines the borehole formed in the earth during the drilling process. This creates an annular area between the casing and the borehole, which is filled with cement to further support and form the wellbore.
Some wells are produced by perforating the casing of the wellbore at selected depths where hydrocarbons are found. Hydrocarbons migrate from the formation, through the perforations, and into the cased wellbore. In some instances, a lower portion of a wellbore is left open, that is, it is not lined with casing. This is known as an open hole completion. In that instance, hydrocarbons in an adjacent earth formation migrate directly into the wellbore where they are subsequently raised to the surface, typically through an artificial lift system.
Junctions between wellbores are commonplace and are useful to reduce costs associated with drilling, to more completely access a formation and to permit multiple formations to be accessed from a single central wellbore. Typically, a lateral wellbore is formed from a central wellbore at some predetermined location with the use of a whipstock or some other type of diverter. The lateral wellbore may be formed along with the central wellbore or it may be formed at a later time when the need arises to access some other formation or some other portion of a formation already being produced. When lateral wellbores are drilled from an existing, cased wellbore, a window is formed in a wall of the casing by milling and then the lateral wellbore is drilled through the window.
However the lateral wellbore is formed, the junction between it and the central wellbore becomes a critical part of the well. In some instances, the lateral wellbore is left unlined and a tubular string is inserted therein to transport wellbore fluids. In other cases, a screen type tubular is inserted into the wellbore to collect fluids that migrate from a surrounding formation. In still other cases, the lateral wellbore is lined with a tubular that is centered in place and perforated at some point to permit the introduction of hydrocarbons. In some cases, it is important to hydraulically isolate a lateral wellbore from the central wellbore. Towards this end, hardware has been developed that is insertable into the area of the junction with tubular members that provide connection means for tubulars running up and down the central wellbore and running out into the lateral wellbore. Through the use of packers and seals, the wellbores can be “plumbed” (or “plugged”) in a variety of ways that prevent the co-mingling of fluids between wellbores or portions of the wellbores. A variety of completion options are employed, including the use of a shared production string for delivering production from producing zones in both the primary and lateral wellbores to the surface. Alternatively, separate production tubulars may be used. In any event, it is oftentimes desirable to place sand screens at the actual zones of production in the primary and lateral wellbores.
Because of their complexity, these junction-lining devices are very expensive to manufacture and their insertion into a wellbore is complex. More importantly, it is not always necessary or even desirable to utilize a device in a wellbore junction that prevents commingling of fluids. Sometimes, the only need is provide some type of structure that will enhance the strength of the junction while not reducing the internal diameter of the wellbores. For example, junctions that are left completely unlined are more likely to suffer cave in or be adversely affected by pressure spikes from one of the wellbores or from a surrounding formation. Additionally, unlined wellbores have no means to prevent solids from entering the junction and interfering with the production of liquid hydrocarbons. In that respect, an open hole leaves aggregate material, including sand, free to invade the wellbore.
Sand production can result in premature failure of artificial lift and other downhole and surface equipment. Sand can build up in the borehole and tubing to obstruct fluid flow. Particles can compact and erode surrounding formations to cause liner and casing failures. In addition, produced sand becomes difficult to handle and dispose of at the surface. Ultimately, open holes carry the risk of complete collapse of the formation into the wellbore.
Heretofore, gravel packs have been utilized in wells to preserve the integrity of the formed borehole, and to prevent the production of formation sand. In gravel packing operations, a pack of gravel, e.g., graded sand, is placed in the annulus between a perforated or slotted liner or screen and the walls of the wellbore in the producing interval. The resulting structure provides a barrier to migrating sand from the producing formation while allowing the flow of produced fluids.
While gravel packs inhibit the production of sand with formation fluids, they often fail and require replacement due, for example, to the deterioration of the perforated or slotted liner or screen as a result of corrosion or the like. In addition, the initial installation of a gravel pack adds considerable expense to the cost of completing a well. The removal and replacement of a failed gravel pack is even more costly.
To better control particle flow from unconsolidated formations, an improved form of well screen has been recently developed. The well screen is known as an expandable sand screen, or “ESS tool.” The ESS is run into the wellbore at the lower end of a liner string and is expanded into engagement with the surrounding formation, thereby obviating the need for a separate gravel pack. In general, the ESS is constructed from three composite layers, including a perforated base pipe, a protective, slotted outer shroud, and an intermediate filter media. The filter media allows hydrocarbons to invade the wellbore, but filters sand and other unwanted particles from entering. Both the base pipe and the outer shroud are expandable, with the woven filter being arranged over the base pipe in sheets that partially cover one another and slide across one another as the sand screen is expanded.
The issues related to unlined junctions are most critical during the time a lateral wellbore is being drilled; long before a conventional junction support could be installed. An operator may want to produce fluids from a formation adjacent the wellbore junction and it is therefore desirable to permit fluids to pass into the wellbore at the junction. However, known hardware used to form the junction is comprised of solid metal materials. Thus, production from the formation at the point of the junction itself has heretofore been impossible. Additionally, it is not unusual to produce from a single formation that is intersected by both the central and lateral wellbores. In these cases, there is no reason to prevent co-mingling of the fluids between the wellbores. Finally, there are instances when cemented junctions become brittle or are damaged by pressure differentials. In these instances, some type of support placed in the junction prior to cementing could serve as a reinforcement of the cement and provide a longer lasting more robust junction.
A further benefit may be gained from using perforated junction hardware even if production from the junction is not desired. Fluid permeable junction hardware will not have to sustain high external formation pressure or contain high internal pressure which could damage solid junction hardware.
Accordingly, a need exists for a method and apparatus for completing a wellbore wherein support is provided for the junction in a multilateral wellbore. Further, a need exists for junction hardware that is not fluid sealed. Still further, a need exists for a junction fabricated from an expandable sand screen so as to prevent sand from entering the production string or otherwise traveling to the surface and being produced.